Lice infestations (pediculosis) are infections of the skin, hair, or genitalregion caused by lice living directly on the body or in hats or other garments. Lice are small wingless insect-like parasites with sucking mouthparts thatfeed on human blood and lay their eggs on body hairs or in clothing. The name pediculosis comes from the Latin word (lousy).
Lice infestations are not dangerous infections by themselves. It is, howevera serious public health problem because some lice can carry organisms that cause other diseases, including relapsing fever, trench fever, and epidemic typhus. Although trench fever is self-limiting, the other two diseases have mortality rates of 5%-10%. Pubic lice are often associated with other sexually transmitted diseases (STDs) but do not spread them.
Lice infestations are frequent occurrences in areas of overcrowding or inadequate facilities for bathing and laundry. They are often associated with homelessness in the general population or with military, refugee, or prisoner camps in war-torn areas. All humans are equally susceptible to louse infestation;the elderly, however, are more vulnerable to typhus and other diseases carried by lice.
The symptoms of lice infestations vary somewhat according to body location, although all are characterized by intense itching, usually with injury to theskin caused by scratching or scraping. The itching is an allergic reaction toa toxin in the saliva of the lice. Repeated bites can lead to a generalizedskin eruption or inflammation.
Head lice is caused by Pediculosis humanus capitis, the head louse. Head lice can be transmitted from one person to another by the sharing of hats,combs, or hair brushes. Epidemics of head lice are common among school-age children from all class backgrounds in all parts of the United States. The head louse is about 1/16 of an inch in length. The adult form may be visible onthe patient's scalp, especially around the ears; or its grayish-white nits (eggs) may be visible at the base of the hairs close to the scalp. It takes between three and 14 days for the nits to hatch. After the nits hatch, the lousemust feed on blood within a day or die.
Head lice can spread from the scalp to the eyebrows, eyelashes, and beard inadults, although they are more often limited to the scalp in children. The itching may be intense, and may be followed by bacterial infection of skin thathas been scratched open. Another common complication is swelling or inflammation of the neck glands. Head lice do not spread typhus or other systemic diseases.
Infestations of body lice are caused by Pediculosis humanus corporis,an organism that is similar in size to head lice. Body lice, however, are rarely seen on the skin itself because they come to the skin only to feed. Theyshould be looked for in the seams of the patient's clothing. This type of infestation is associated by wearing the same clothing for long periods of timewithout laundering, as may happen in wartime or in cold climates; or with poor personal hygiene. It can be spread by close personal contact or shared bedding.
Patients with body lice often have intense itching with deep scratches aroundthe upper shoulders, flanks, or neck. The bites first appear as small red pimples but may cause a generalized skin rash. If the infestation is not treated, the patient may develop complications that include headache, fever, and bacterial infection with scarring. Body lice can spread systemic typhus or other infections.
Pubic lice are sometimes called "crabs." This type of infestation is caused by Phthirus pubis and is commonly spread by intimate contact. People can also get public lice from using the bedding, towels, or clothes of an infected person.
Pubic lice usually appear first on pubic hair, but may spread to other partsof the body, particularly if the patient is very hairy. Pubic lice are also sometimes seen on the eyelashes of children born to infected mothers. It is usually easier for the doctor to see marks from the patient's scratching than the bites from the lice, but pubic lice sometimes produce small bluish spots called maculae ceruleae on the patient's trunk or thighs. Pubic lice also sometimes leave small dark brown specks from their own excreted matter on the parts of the patient's underwear that cover the anal or genital areas.
Doctors can diagnose lice infestations from looking closely at the parts of the body where the patient has been scratching. Lice are large enough to be easily seen with the naked eye or a magnifying glass. The eggs of pubic lice aswell as head lice can often be found by looking at the base of the patient'shairs. Pediatricians are most likely to diagnose lice in school-age children.
It is important for doctors to rule out other diseases that can cause scratching and skin inflammation because the medications used to kill lice are verystrong and can have bothersome side effects. The doctor will need to distinguish between head lice and dandruff; between body lice and scabies (a diseasecaused by skin mites); and between pubic lice and eczema. Blood tests or other laboratory tests are not useful in diagnosing lice infestations.
Lice infestations are treated with externally applied medications that eitherkill the lice or prevent them from feeding. Cases of head lice are usually treated with shampoos or rinses containing either lindane (Kwell) or permethrin (Nix). Because lindane is absorbed through the skin, the person giving theapplication should wear rubber gloves and rinse the patient's hair or body completely after use. Following the treatment, nits should be removed from thehair with a fine-toothed comb or tweezers. Lindane is also effective for treating infestations of body or pubic lice, but it should not be used by pregnant women. In most cases one treatment is sufficient, but the medication can bereapplied a week later if living lice have reappeared.
Infestations of body lice can also be treated by washing the patient's clothes or bedding in boiling water, ironing seams with an iron on a high setting,or treating the clothes with 1% malathion powder or 10% DDT powder.
If the patient's eyelashes have been infested, the only safe treatments are either a thick coating of petroleum jelly (Vaseline) applied twice daily for eight days, or 1% yellow oxide of mercury applied four times a day for two weeks. Any remaining nits should be removed with tweezers.
Patients with pubic lice should be examined and tested for other STDs.
For pubic lice, some practitioners of holistic medicine recommend a mixture of 25% oil of pennyroyal (Mentha pulegium), 25% garlic (Allium sativum) oil, and 50% distilled water applied three times in a three-day period, followed by removal of dormant eggs to prevent reinfestation.
Lice can be successfully eradicated in almost all cases, although some casesof lindane-resistant lice have been reported. In general, patients are more at risk from typhus and other diseases spread by lice than from the lice themselves.
There are no vaccines or skin treatments that will protect a person against lice prior to contact. In addition, lice infestation does not provide immunityagainst reinfection; recurrences are in fact quite common. Prevention depends on adequate personal hygiene at the individual level and the following public health measures:
- Teaching school-age children the basics of good personal hygiene, including the importance of not lending or borrowing combs, brushes, or hats.
- Notifying and treating an adult patient's close personal and sexual contacts.
- Examining homeless people, elderly patientsincapable of self-care, and other high-risk individuals prior to hospital admission for signs of louse infestation. This measure is necessary to protectother hospitalized people from the spread of lice.